This invention relates to a process for treating flue gas that contains fly ash and carbon dioxide (CO2). The flue gas may contain nitrogen oxides (NOx), sulfur oxides (SOx), and other compounds and pollutants commonly present in flue gas produced by combustion of pulverized coal or other fossil fuels. The treatment process captures the flue gas components into a solid form.
Fly ash is the finely divided mineral residue resulting from the combustion of pulverized coal in coal-fired power plants. Fly ash consists of inorganic, incombustible matter present in the coal or fuel that has been fused during combustion into a glassy, amorphous structure. Fly ash material is solidified while suspended in the exhaust gases and is collected by electrostatic precipitators or filter bags. They consist mostly of silicon dioxide (SiO2), aluminum oxide (Al2O3) and iron oxide (Fe2O3), and are hence a suitable source of aluminum and silicon for geopolymers. They are also pozzolanic in nature and react with calcium hydroxide and alkali to form cementitious compounds.
Carbon dioxide is a principal reaction product in coal combustion. It is also a “greenhouse gas” believed to contribute to global climate change. Many researchers are seeking means to reduce greenhouse gas emissions by capturing carbon dioxide from large stationary sources, such as power plants.
It is known to remove nitrogen oxides and sulfur oxides from gaseous effluent by an aqueous, alkaline scrubber. The scrubbing solutions may have a high pH, from 7 to 14, and typically from 10 to 14. Slaked lime (Ca(OH)2) is one known example of a scrubbing solution. Dry sorbents and catalytic processes are also known and used to remove nitrogen and sulfur oxides from flue gas.
It would be an advancement in the art to provide a process for treating flue gas that contains fly ash and carbon dioxide such that the flue gas components are captured into a solid form. It would be a further advancement in the art to provide a process that captures carbon dioxide in flue gas to prevent it from contributing to environmental greenhouse gases. It would be yet another advancement in the art to provide a process for treating flue gas that converts fly ash into a usable concrete additive. Such processes are provided herein.